Stents are generally designed as tubular support structures that can be used in a variety of medical procedures to treat blockages, occlusions, narrowing ailments and other problems that restrict flow through body vessels. Typically, a stent is radially compressed to a reduced diameter for transport within a vessel and then radially expanded to contact the vessel wall once in place at a treatment site. Radial compression of the stent is typically carried out in a compression apparatus.
FIGS. 1A and 1B are schematics of a prior art apparatus 10 for radially compressing a stent to a reduced diameter configuration. Referring to FIG. 1A, a cylindrical opening 12 is formed in a sheet 14 sandwiched between a wedge 16 and a support 18. The apparatus 10 employs linear motion of the wedge 16 to alter the diameter of the cylindrical opening 12. By moving the wedge 16 across the support 18 toward or away from the cylindrical opening 12, the size of the opening 12 can be reduced or expanded, as shown schematically in FIG. 1B. Accordingly, a stent placed in the cylindrical opening 12 may be radially compressed as the wedge 16 moves across the support 12 and decreases the size of the opening 12. The support 18 remains stationary as the wedge 16 moves.
To facilitate motion of the wedge 16, a first control arm 20 is connected to the wedge 16 at one end and to a linear bearing 22 at the other end. A second control arm (not visible in figure) is disposed behind the first control arm 22 and connected to a second linear bearing (also not visible). Each linear bearing 22 is disposed about a cylindrical shaft 24 positioned perpendicular to the cylindrical opening 12. When the linear bearings 22 are moved along their respective shafts 24, the control arms 20 drive the wedge 16 across the support 18, thereby changing the size of the cylindrical opening 12.
It is important to be able to control the gap or spacing between the wedge 16 and the support 18. Any misalignments of the linear bearings 22 with respect to the support 18 or each other may cause the spacing to vary as the bearings 22 travel along their respective cylindrical shafts 24. If the gap is too large, a stent placed in the cylindrical opening 12 may be squeezed between the opposing portions of the sheet 14 during the compression. If the gap is too small, frictional forces may increase. It is desirable to use small, lightweight linear bearings to minimize bearing friction and permit high resolution feedback of the compression forces being applied to the stent; however, such linear bearings 22 tend to flex during the compression of larger stents, allowing the size of the gap between the wedge 16 and the support 18 to increase. Consequently, larger, stiffer linear bearings 22 are generally employed, and the distance between the support 18 and the bearings 22 is minimized. The forces needed to move the massive bearings 22 can be so large, however, that the operator's ability to monitor compression forces at the desired resolution may be impaired. Also, at short distances between the bearings 22 and the support 18, the stent can be exposed to contamination from the bearing surfaces, and it may be problematic to carry out the compression in a controlled atmosphere and/or at tightly controlled or extreme temperatures.
Due to the shortcomings of the prior art apparatus described above, it would be advantageous to develop an improved apparatus and method for compressing a stent.